In many fluid distribution systems—such as may be found in the semiconductor industry—fluid valves are often exposed to a variety of harsh chemicals, including acids and solvents. To withstand these harsh chemicals, a valve may be constructed of chemically resistant materials such as, for example, fluoropolymer materials. Fluoropolymer materials commonly used in the fabrication of corrosion resistant valves include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy), and PVDF (polyvinylidene fluoride), as well as others. A wide variety of valve types fabricated from such fluoropolymer materials, as well as other corrosion resistant materials, and exhibiting high corrosion resistance are commercially available, including ball valves, diaphragm valves, poppet valves, sleeve valves, and pinch valves.
An important concern in fluid distribution systems, especially for integrated circuit manufacturers, is the generation of particulates during valve actuation, as these particulates can enter the fluid stream flowing through the valve and migrate to other portions of the fluid distribution system. Particulates suspended in a fluid may cause corrosion and abrasion of the various components (e.g., valves, flow meters, sensors, tubing) comprising a fluid distribution system and, further, such suspended particulates may contaminate production parts and materials during manufacturing, resulting in poor quality or damaged products. To minimize particulate generation, valve types exhibiting low particulate generation (e.g., diaphragm, poppet, sleeve, and pinch valves) are used to control fluid flow, while those valve types exhibiting high particulate generation (e.g., ball valves) are typically avoided.
Also of concern for many fluid distribution systems is abrasion and wear caused by the flow of slurries—e.g., abrasive slurries used in lapping processes such as chemical-mechanical planarization (CMP)—and other fluids containing abrasive particles. A typical ball valve, for example, includes one or more seals that impinge upon the valve's ball to form a seal therewith when the ball valve is in the closed condition. The material properties (e.g., low hardness) dictated by the sealing function of the seals are, in many instances, inconsistent with those characteristics (e.g., high hardness) that provide resistance to abrasion. Thus, the seals of a ball valve—as well as other components of a fluid distribution system—are often susceptible to abrasion and wear when used to control the flow of abrasive slurries.
Although diaphragm, poppet, sleeve, and pinch valves provide minimum particulate generation during actuation, as noted above, each of these valve types exhibits undesirable characteristics. All of these valves typically have a large and bulky external structure—in which, for example, the valve actuation mechanism protrudes perpendicular from the axis of flow through the valve—making it difficult to closely space a plurality of flow lines. The inability to co-locate multiple flow lines in close proximity to one another is problematic where “real estate” available for a fluid distribution system is minimal, as is often the case in semiconductor chip manufacturing facilities.
Some of the aforementioned valves, such as diaphragm and poppet valves, provide a flow path extending therethrough that exhibits multiple fluid direction changes and/or that exhibits a reduction in flow path cross-sectional area. Such fluid direction changes and flow path reductions—whether either of these characteristics is present individually or both are present in combination—provide a flow restriction that limits flow through the valve. Also, a flow path having multiple fluid direction changes may exhibit stagnant regions where fluid may become trapped.
To overcome (or avoid) the internal restrictive geometry of diaphragm and poppet valves, a common solution was to use an oversize valve (e.g., using a ¾″ valve for a ½ pipe installation) in combination with adapters to install the valve. However, the use of an oversize valve increases the space necessary for installation, which is especially problematic when numerous valves must be co-located in close proximity, as noted above. Another typical solution was to altogether avoid diaphragm and poppet valves and use valves providing better flow characteristics. A type of valve providing improved flow characteristics is the ball valve but, as previously suggested, ball valves exhibit relatively high particulate generation and may also be susceptible to wear from abrasive slurries.
A conventional pinch valve comprises a flexible, tubular sleeve that is compressed, or pinched, by a mechanical actuator (e.g., a spring, a push-rod, or a combination thereof) to inhibit the flow of fluid through the tubular sleeve. Conventional sleeve valves similarly comprise a flexible, tubular sleeve that is compressed under application of, for example, hydraulic (or pneumatic) fluid pressure. Generally, for both pinch and sleeve valves, the tubular sleeve must be compressed to a fully collapsed state to close the valve. Pinch and sleeve valves provide relatively good flow characteristics (e.g., low flow restriction) and minimal particulate generation; however, each of these valve types exhibit a number of disadvantages that make them unsuitable for many applications.
Both pinch and sleeve valves operate insufficiently, or not at all, under vacuum conditions, especially for larger diameter valves that may not exhibit sufficient resiliency to overcome a vacuum and decompress without assistance. To decompress and open a pinch valve subjected to a vacuum, retraction forces (i.e., forces directed radially outward) must be applied to the outer surface of the tubular sleeve and, for large diameter pinch valves, the retraction forces required to overcome a vacuum may be relatively large. To apply such retraction forces, lugs or other grasping devices must be secured to the outer surface of the tubular sleeve, such that the pinch valve's mechanical actuator can grasp the wall of the tubular sleeve to retract and open the valve when vacuum conditions exist. The lugs are typically separate parts that must be attached to the outer surface of the tubular sleeve using a bonding or welding process. The bond between the lugs and the tubular sleeve, especially for polymer materials commonly used in corrosion resistant valves, may be relatively weak in comparison to the forces necessary to overcome a vacuum. Accordingly, severing of the bond between the lugs and tubular sleeve often occurs when a pinch valve is operated in a vacuum, resulting in a failure of the pinch valve to open. A conventional sleeve valve does not operate at all under a vacuum, as retraction forces can not be applied to the tubular sleeve by application hydraulic or pneumatic fluid pressure to the sleeve's outer surface.
The mode of actuating pinch and sleeve valves—e.g., full compression or collapse of the tubular sleeve to completely restrict fluid flow therethrough—may itself lead to a number of problems. In particular, pinch and sleeve valves may not seal completely when closed. Also, pinch and sleeve valves exhibit poor fatigue life due to the necessity of collapsing the tubular sleeve, which results in sharp bends in the wall of the sleeve. Further, due to the difficulty of fully collapsing (and decompressing) a large diameter tubular sleeve, pinch and sleeve valves are difficult to manufacture in large sizes (e.g., 1″ diameter and above).
The lack of a fail safe actuation mechanism is an additional problem exhibited by some conventional fluid valves. A typical sleeve valve, for example, is open in the relaxed or uncompressed state and provides no restriction to flow. Upon compression of the sleeve valve's flexible sleeve by a hydraulic (or pneumatic) actuator that exerts fluid pressure against the flexible sleeve, the flexible sleeve deforms to a collapsed state in which fluid flow through the sleeve is restricted. However, because the sleeve valve is open in the relaxed state (i.e., normally open) and fluid pressure must be maintained against the flexible sleeve to maintain the sleeve valve in the closed condition, the sleeve valve will fail to restrict fluid flow when fluid pressure in the hydraulic actuator is lost and, accordingly, the sleeve valve is not fail safe.